Dimethylformamide-aliphatic diester spinning solutions of polyacrylonitriles



No Drawing. Application November 13,1953

' Serial No- 39 ,045

Claims priority, application Germany December 18, 1952 2 Claims. (Cl.260--31.6)

This invention relates to the production of filaments frompolyacrylonitrile or from mixed polymerisates containingpolyacrylonitrile, dissolved in a solvent consisting of, or containing,dimethylformamide.

It is an object of this invention to provide a solvent for thepolymerised compounds which is free from the tendency of allowing thematter dissolved therein to swell or form jellies and to thereby disturbthe spinning operation.

It is a further object of this invention to provide a solvent for thematerials mentioned above which does not lead to discoloration of thefilaments.

It is a particularly important object of this invention to improvesolutions in dimethylformamide, which is a particularly good solvent forthe said materials, by doing away with any tendency of jelly-formationand discoloration.

As is well known to those skilled in the art, the number of solventssuitable for practical use in the preparation of spinning solutions frompolyacrylonitrile or mixed polymerisates containing this compound isparticularly limited. It is equally known that dimethylformamide is onthe Whole a satisfactory solvent, but requires being improved in severaldirections. Thus, for instance, the dispersion which is first formedwhen trying to dissolve the polyacrylonitrile in dimethylformamide,causes a tendency of the nitrile to form a jelly and renders thespinning solution inhomogenous to the extent that the spinning processis disturbed and the filament breaks.

Apart from this, solutions of the polyacrylonitrile in dimethylformamidehave hitherto suffered from slight discolorations of the spinningsolution and of the filaments produced from them.

I have now found that altogether satisfactory spinning solutionscontaining dimethylformamide as predominant solvent can be obtained byadding to this solvent a certain quantity of an aliphatic diesterconstituted according to the formula wherein R stands for --CH:- or forOH H8 and n is an integer ranging from zero to two.

For instance, if R is replaced by the methylene group (CH2), thecompound to be added to the dimethylformamide ismethyleneglycol-diacetate, methyleneglycoldipropionate ormethyleneglycol-dibutyrate.

If R is replaced by the ethylidene group I CH3 there are obtained thecorresponding ethylidene compounds, viz. ethylideneglycol-diacetate,ethylideneglycoldipropionate or ethylideneglycol-dibutyrate.

The mixtures of dimethylformamide with one of the nited States Patent2,814,603 Pa ent-e5 Ne 2.6 1.95.

ubsta tors id. o ns anc a mixtu o im th formamide with'inethyleneglycol-diacetate, form with polyacrylonitrile, or? itsmixtureswith other polymerisates teih 's i jia tor' spinning solu i n Ihave found that the best solvent is obtained if 5-20 percent by weight,and preferably 7 -10 percent of the diester calculated onthe' weight ofthe dimethylformamide, are added .to it.

When using solvent mixtures of the kind aforesaid in the preparation ofspinning solutions from polyacrylonitrile or mixtures of the nitrilewith other polymerisates, the tendency of the polymers for the formationof jellies is altogether doneaway with and the disturbances arising whenoperating with dimethylformamide alone are avoided altogether.

I have further found that the spinning solution is improved also in thatneither the solutions nor the filament obtained with their aid do showany discoloration worth speaking of.

I have noticed also that the use of mixtures of the kind forming theobject of this invention increases the stretching capacity of thefilaments obtained from the solutions.

In operating this invention, I may, for instance, proceed as follows:

Example 1 22 parts by weight of polyacrylonitrile, having a K-value of87, were added to 78 parts of a solvent mixture consisting of 85 percentby weight dimethylformamide and 15 percent methyleneglycol-diacetate.

The polymerisate was stirred according to well-known methods to form adispersion which then dissolved in the solvent mixture under heating.The solution thus obtained yielded an unobjectionable liquid of highfilament-forming capacity. The filaments spun from it had a particularlyhigh stretching capacity and stretching velocities of 300-350 meters perminute could be employed.

The filaments possessed particularly favorable mechanical properties andshowed a resistance to breaking of 42 kilometers.

In comparison therewith, when using the same starting products, however,without the addition of methyleneglycol-diacetate the dispersion formedin the solvent showed an undesirable tendency of jelly-formation and thefilaments obtained from the solution could be stretched only at thenormal velocity of 200 meters per minute. Their resistance to breakingamounted to 38 kilometers.

Example 2 19 parts by weight of a co-polymer formed of 95 percentacrylonitrile and 5 percent vinylimidazol, having a K-value of about 92,was stirred to form a dispersion in percent of a solvent mixtureconsisting of percent by weight dimethylformarnide and 20 percentethylideneglycol-diacetate. After heating to fusion temperature alight-colored solution was obtained, which could be spun without anydisturbances. The filaments from the solution could be stretched at avelocity of 250-300 meters per minute. The resistance to breakingextended to 40 kilometers.

Example 3 21 parts by weight of a co-polymer formed from percent byweight acrylonitrile and 10 percent acrylic acid amide (K-value near 87)were dispersed in 79 parts of a solvent mixture formed of 82 percentdimethylformamide and 18 percent methyleneglycol-dipropionate.

In following the methods reported with reference to Example 1 a solutionof high filament-forming capacity was obtained. The resistance of thefilaments extended to about 42 kilometers.

Various changes may be made in the proportions and compositions of thematerials and solvents reported in the foregoing specification withoutdeparting from the invention or sacrificing the advantages thereof.

I claim:

1. The process of preparing spinning solutions which comprisesdissolving a member selected from the group consisting ofpolyacrylonitrile and a copolymer of acrylo nitrile with anotherpolymerizable unsaturated compound in minor proportion in a solventcomprising dimethylformamide in admixture with from 5 to 20 percent byweight of an aliphatic diester of the formula and n has the value zeroto two inclusive.

2. The process of preparing spinning solutions which 4 comprisesdissolving a member selected from the group consisting ofpolyacrylonitn'le and a copolymer of acrylonitrile with anotherpolymerizable unsaturated compound in minor proportion in a solventcomprising dimethylformarnide in admixture with from 7 to 10 percent byweight of an aliphatic diester of the formula CI'h-(CH2)11,.C0.0.R.O.CO.(CH2)nCH3 wherein R is a member of the group consisting of -OH;- and--0H- and n has the value zero to two inclusive.

References Cited in the file of this patent UNITED STATES PATENTS2,589,055 Coover et a1 Mar. 11, 1952

1. THE PROCESS OF PREPARING SPINNING SOLUTIONS WHICH COMPRISESDISSOLVING A MEMBER SELECTED FROM THE GROUP CONSISTING OFPOLYACRYLONITRILE AND A COPOLYMER OF ACRYLONITRILE WITH ANOTHERPOLYMERIZABLE UNSATURATED COMPOUND IN MINOR PROPORTION IN A SOLVENTCOMPRISING DIMETHYLFORMAMIDE IN ADMIXTURE WITH FROM 5 TO 20 PERCENT BYWEIGHT OF AN ALIPHATIC DIESTER OF THE FORMULA